Drongos
(Dicruridae)
Class: Aves
Order: Passeriformes
Suborder: Passeri (Oscines)
Family: Dicruridae
Thumbnail description
Glossy black, fork-tailed, starling-sized songbirds that live in trees and hawk for insect food from vantage perches
Size
7–25 in (18–63 cm), including tail; 0.8–4.8 oz (25–135 g)
Number of genera, species
2 genera; about 22–24 species
Habitat
Tropical and subtropical forest to forest edge, open woodland, and gardens
Conservation status
Endangered: 2 species; Near Threatened: 4 species
Distribution
Old World tropics and subtropics, from sub-Saharan Africa to southern Asia southeast through Indonesian archipelagos to Solomon Islands and Australia
Evolution and systematics
Long thought to be related to starlings and orioles, the drongos have been shown by recent molecular and skeletal research to be nested among the Australasian monarch flycatchers (family Monarchidae) and related to corvoid songbirds. Unlike starlings but like monarchs, they have a single pneumatized fossa in the head of the humerus; and like monarchs but unlike orioles, they have a heavily ossified nasal cavity and narrow ectethmoidal plate. To manhandle large and hard-cased insect food, they also have an extended bony plate in the roof of the palate, thickened nasal bars, and a large depression in each temple flanked by a long zygomatic process for the attachment of powerful jaw muscles; drongos are strong-billed birds. Outwardly, monarchs also match drongos in their glossy black plumages, arboreal hawking behavior, flimsy nests perched in horizontal tree forks, and reddish-marked eggs.
The drongo-monarch group is a core branch in a massive radiation of crow-like songbirds that appears to have exploded in Australia some 20–30 million years ago, and quickly spread through the Old World tropics. The drongo lineage would have been in the vanguard, reaching Africa and radiating into 11–13 species in Southeast Asia and fringing archipelagos. Left behind in montane New Guinea, signposting the source of radiation as it were, was the pygmy drongo (Chaetorhynchus papuensis), the most monarch-like and ancestrally structured drongo of all. The fossil record, limited to the Pleistocene for drongos, preserves little of this information.
Today there are 22–24 species of drongos, one in the genus Chaetorhynchus and the rest in the larger but still tight-knit genus Dicrurus. Only the taxonomy of the balicassius-hottentotottus species-group in the Indo-Australasian archipelagos is seriously controversial, opinions being divided over whether there are anywhere from four to eight species in the 36 taxon complex.
Physical characteristics
Resembling stream-lined, long-tailed starlings, drongos are a picture in black—black in plumage, bill, and feet—except for the gray ashy drongo (D. leucophaeus) in Southeast Asia; immatures are duller and sootier, and in some species faintly scalloped, barred, or spotted paler. Eyes, brilliant red in most species (though whitish or brown in some forms), provide the only color contrast; immatures are brown-eyed without exception. Plumage is extensively glossed in green, blue, or purplish sheens, the gloss sometimes spangling hackles on head and breast. Some species are also crested. Crests vary, according to species, from a short tuft of erect feathers on the forehead to bare hair-like plumes or a mane of broadened curled feathers curving back over the head.
Bills are stout, deep, and rather aquiline, well-notched for grasping prey, and clothed with dense, forward-directed bristles at the base. The bristles, which hide slit-like nostrils, are thought to protect the face from retaliation by captured prey; in Chaetorhynchus they extend to the bill tip. Feet are short but strong, and with the toes about as long as the scutellate "leg," are better fitted for perching than movement. Adapted for aerial maneuvers, wings are rather long and pointed, with 10 primaries (tenth well-developed) and nine secondaries plus a remicle. It is the tail that sets drongos apart from other songbirds. Sometimes square-tipped but usually long and forked, it comprises 12 feathers in Chaetorhynchus and only 10 in Dicrurus, and is often diversely modified by a great lengthening and curling of the outermost pair of feathers. In two species, these plumes are largely bare of webbing except for spatula-like tips; but the function of such modification is not clear. Tails in all species are at least as long as the body, and up to three times as long, even more, in some. Because of this, drongos vary enormously in length, from 7 in to over 23.5 in (18–60 cm).
Distribution
Drongos occur throughout the Old World tropics and subtropics: there are four species in tropical and subtropical sub-Saharan Africa, four in Madagascar and nearby island archipelagos, 11–13 centered in southern and Southeast Asia, from east Iran and India to south Manchuria (Bol Hai), the Philippines and central Indonesian archipelagos, and just four (possibly five) from the east Indonesian Archipelagos to the Solomon Islands and north and east Australia. Most species are sedentary, but populations of those that breed in more temperate latitudes, of the black drongo (Dicrurus macrocercus), ashy drongo, and hair-crested drongo (D. hottentottus) in China, and the spangled drongo (D. bracteatus) in east Australia, are migratory, shifting to the tropics in winter.
Habitat
Tropical and subtropical forests, secondary growth, and forest edge to mangroves, open woodlands, and even urban environs are the habitat of drongos, according to species. Some, such as the New Guinean pygmy drongo, the African shining drongo (D. atripennis), and Sulawesi drongo (D. montanus) are confined to primary rainforest; but others, notably the widespread Asian black drongo, occupy towns, gardens, and open areas, and are a familiar sight perched on electric lines. Where different species occur together, they co-exist by occupying different habitats. Thus in Southeast Asia, the black, ashy, and greater racket-tailed (D. paradiseus) drongos live in more open woods, urban areas, and marshes, while the bronzed (D. aeneus), lesser racket-tailed (D. remifer), and hair-crested drongos keep to denser forests, often replacing one another altitudinally. In Africa, square-tailed (D. ludwigii), velvet-mantled (D. modestus), and shining (D. atripennis) drongos replace one another in different strata in different structural habitats. Wherever they occur, both resident and migratory populations are well dispersed at densities of about 5–40 birds per mi2, depending on productivity and connectivity of habitat.
Behavior
Solitary except when paired or in family groups during breeding, drongos are nevertheless showy and noisy birds. Their daily routine is one of perching in the bare middle tiers of trees or their edges, on exposed vantage points from which to sally out in buoyant but agile evolutions on the wing after food, and then return. On the perch they sit upright, long tail hanging down and sporadically waving or twitching from side to side. All movement is on the wing, the birds never moving about on foot. To bathe, they plunge-dive from a perch or flight. Among the first birds to rise before dawn and the last to go to roost, drongos call regularly throughout the day year round, mostly from perches. The calls, of a great variety of grating chatters, creaking hinge notes, discordant chuckles, and melodious whistles, usually have something of a metallic twang; and each song stanza is rarely longer than five or six quick syllables. Some species, perhaps all, are accomplished mimics. Although some species are more retiring than others, all are rather quarrelsome, and are bold and pugnacious in defense of territory. They will attack and chase off birds as large as crows and medium-sized raptors, and mob owls, hornbills, and small predatory mammals.
Feeding ecology and diet
Drongos feed by hawking from perches, either catching prey in the air or picking it from the surface of leaves, branches, or ground. They often join flocks of mixed insectivorous birds quartering their habitat, benefiting from insects disturbed by other species. Drongos of more open habitat also converge opportunistically on fires to snap up insects flushed by flame and smoke. They take an enormous variety of arthropods, many of them large and hard-shelled and most of them flying: grasshoppers, crickets, beetles, mantids, cicadas, moths and butterflies, dragonflies, ants, and even venomous Hymenoptera (wasps and bees), occasional arachnids, and sometimes small birds; they also rifle blossoms for nectar. Termite emergences have a special attraction. Large items are carried in the foot and held by it at a perch, to be torn apart with the bill; moths, butterflies, and dragonflies have their wings torn off before being swallowed.
Reproductive biology
Monogamous and aggressively territorial, drongos breed in dispersed pairs, some species often rearing several broods in a season. In most regions, breeding peaks over spring and summer, particularly in temperate zones north and south of the tropics, where post-breeding molt is also more consistently seasonal. Little is known of courtship, which may comprise little more than head bobbing and bowing, and duetting and counter-singing, as male and female sit together. Both sexes share all nesting duties from nest construction to incubation and rearing of young. Nests are flimsy, shallow saucers of loosely but neatly intertwined rootlets, tendrils and, in some species, leaves, lined with finer material and sometimes wool, often bound on the outside with cobweb and camouflaging lichen, and hung in a horizontal fork at the end of a branch at 6.6–82 ft (2–25 m) above the ground. In clutches of two to five, eggs are salmon-buff to pale cream or pinkish white, covered in freckles and small blotches of brownish red, black, or umber and lilac according to species, with underlying smudges and streaks of pale gray and purple; they measure about 0.8–1.2 by 0.5–0.8 in (20–30 by 15–21 mm). In the African fork-tailed drongo (D. adsimilis), eggs hatch in 16–17 days and young fledge in another 17–18 days.
Conservation status
Drongo survival is only threatened when total treed habitat is limited in area. This is the case for species confined to small islands, such as those in the Comoro group off the central east coast of Africa. Both the Comoro drongo (D. fuscipennis) on Grand Comoro Island and Mayotte drongo (D. waldenii) on Mayotte Island are listed by IUCN as Endangered. Two of the four species in the Near Threatened category also occur on small islands: D. aldabranus on Aldabra Island just north of the Comoros, and D. andamanensis in the
Andamans in the Bay of Bengal. Of the other two, the velvet-mantled drongo (D. modestus) occurs in west central Africa and the Sumatran drongo (D. sumatranus) is endemic to Sumatra, Indonesia. Destruction of forest habitat is their primary threat.
Significance to humans
Despite their extrovert behavior, drongos have made little impact on human society and culture except for the black drongo. This species, a familiar urban commensal across southern Asia, is often cultivated in captivity there. Black drongos from Taiwan were also introduced successfully to Rota in the southern Marianas (Micronesia) in the 1930s, and from there had colonized neighboring Guam by the early 1960s. Its other vernacular name—king crow—celebrates its nerve and pugnacity in driving off predatorial birds much larger than itself.
Species accounts
Pygmy drongoSquare-tailed drongo
Ribbon-tailed drongo
Ashy drongo
Greater racket-tailed drongo
Black drongo
Resources
Books:Ali, S., and S.D. Ripley. Handbook of the Birds of India and Pakistan, Vol. 5. Bombay: Oxford University Press, 1972.
Coates, B.J. The Birds of Papua New Guinea. Vol. 2. Alderley, Qld: Dove Publications, 1990.
Du Pont, J.E. Philippine Birds, Monograph Series No. 2. Wilmington: Delaware Museum of Natural History, 1971.
Fry, C.H, S. Keith, and E.K. Urban, eds. The Birds of Africa. Vol. VI. New York: Academic Press, 2000.
MacKinnon, J., and K. Phillipps. A Field Guide to the Birds of Borneo, Sumatra, Java, and Bali. Oxford: Oxford University Press, 1993.
Schodde, R., and S.C. Tidemann, consultant eds. Reader's Digest Complete Book of Australian Birds. 2nd ed. Sydney: Reader's Digest Services, 1986.
Schodde, R., and I.J. Mason. The Directory of Australian Birds, Passerines. Melbourne: CSIRO Publishing, 1999.
Sibley, C.G., and J.E. Ahlquist. Phylogeny and Classification of Birds. New Haven: Yale University Press, 1990.
Sibley, C.G., and B.L. Monroe, Jr. Distribution and Taxonomy of Birds of the World. New Haven: Yale University Press, 1990.
Smythies, B.E. The Birds of Borneo. 3rd ed. Kota Kinabalu and Kuala Lumpur: The Sabah Society and the Sabah Nature Society, 1981.
Vaurie, C. "Dicruridae." Check-List of Birds of the World. Vol. 3. Cambridge, MA: Museum of Comparative Zoology, 1962.
Periodicals:Beehler, B.M. "Notes on the Mountain Birds of New Ireland." Emu 78 (1978): 65–70.
Vaurie, C. "A Revision of the Bird Family Dicruridae." Bulletin of the American Museum of Natural History 93 (1949): 199–342.
Organizations:Australian National Wildlife Collection. GPO Box 284, Canberra, ACT 2601 Australia. Phone: +61 2 6242 1600. Fax: +61-2-6242-1688.
Other:Australian Biological Resources Study. Canberra, ACT, Australia.
UNEP World Conservation Monitoring Center. Threatened Animals of the World. . January 2002.
[Article by: Richard Schodde, PhD]
